PORTLAND, Ore. - A couple on a Sunday fishing trip on the Columbia River near the Portland airport made a grisly discovery.

Now, police have started a homicide investigation.

The couple spotted a bag floating in the river while fishing off the east side of Government Island, and what they found inside it prompted them to call police.

Investigators say the bag held human remains and they are certain of one thing: foul play is involved.

Jason Gates of the Multnomah County Sheriff's Office says many other questions remain unanswered, including who the remains belong to, how long they've been in the water, and if the bag was previously sunk and then refloated itself.

Detectives will be back in the area to look for clues, but the river poses several investigative challenges.

"If you have a crime scene at a house or a static location," Gates says, "it's a lot easier to try and come up with a timeline and what exactly happened and gather evidence."

The Multnomah County medical examiner is now looking over the remains.
    
Investigators have not said if the remains belong to a man or woman.

Investigators say the remains found Sunday are not linked to a case in 2003 that also involved human remains found in the river.

The Multnomah County Sheriff's Office is asking anyone with information to give them a call.